Method for determining pore pressure in oil and gas wells using basin thermal characteristics

ABSTRACT

This inventive method provides a novel way of modeling basins in planning the drilling of crude oil and natural gas wells by accounting for thermodynamic considerations in tracking the pore pressure of a location of interest. By plotting the energy gradients, heat flux, and thermal conductivity of the location of interest, the user can more accurately identify the location of the Top of Geopressure and additional pertinent information during the well drilling planning process that can reduce costs and increase the safety of the process.

This application claims the benefit of U.S. Provisional PatentApplication No. 62/184,961 filed on Jun. 26, 2015. The disclosure of thereferenced application is hereby incorporated herein in its entirety byreference.

BACKGROUND OF THE INVENTION

The present invention relates to the field of safety and accuracy incrude oil and natural gas well drilling, particularly the use ofthermodynamic principles in order to develop a new method for safely andaccurately conducting crude oil and natural gas well drilling.

Well blowouts are caused by the uncontrolled release of crude oil ornatural gas well after a well's pressure control systems have failed.Given the threat to life and adverse impact on property and environmentthat a blowout can have, significant planning and precautions areundertaken when drilling the well. As part of safe drilling practices,persons who drill wells must consider several factors when planning awell, including pore pressure determination. The Pre-drill estimation ofpore pressure and fracture gradient analysis is the bedrock of thewell-planning process. Optimal pore pressure and fracture gradientestimates rely on the accuracy of overburden gradient calculations,which signify the characteristics of a given basin. If overburden orvertical stress gradient calculations are off, then pore pressure andfracture gradient estimates may be grossly underestimated oroverestimated, both of which can result in severe wellbore instabilityand/or well control issues.

“Geopressure” refers to a subterranean earth formation where the fluidpressure of the pores exceeds hydrostatic. More specifically, Terzaghi'sPrinciple states that all quantifiable changes in stress to a soil(e.g., compression, deformation, shear resistance) are a direct resultof a change in effective stress. The effective stress σ′ is related tototal stress σ and the pore pressure u by the relationship σ=σ′+ureading that total stress is equal to the sum of effective stress andpore water pressure.

Subsequently, the above authors defined the effective stress of a systemas the difference between the total overburden of overlying sedimentsand the pressure of fluids occupying the pores of rock material. Laterthe oil and gas industry defined the “normal” pressure as the Salt watergradient or 0.465 psi/ft for the Gulf of Mexico and any pressure inexcess of normal gradient as “abnormal” pore pressure.

Yet, an inherent weakness in Terzaghi's Principle is that it fails toincorporate additional thermally induced pressure into the equation. Inaddition, this theory does not relate the thermal properties of the rockformation and heat flow—that is specific to shale and sandstoneformations—to the location and magnitude of Formation Pore Pressures.Terzaghi's approach to the compaction-dominated system does not need totake into account the effect of “high” Temperature and ThermalConductivity of rock material but it would have been appropriate to haveincluded the cold and low temperatures. This is because unusualpressures are often seen to affect the freeze-thaw cycles which in turnaffect the shape of pores and in places such as Alaska affects certainsurface pressures. For example, the contribution of temperature orgeochemical reactions to the effective stress gradient is notrepresented in either Terzaghi's equation or the publications by theabove mentioned authors.

Although thermodynamic or related properties associated with temperatureare recognized by the petroleum industry; the experts, especially thoseengaged in serious basin modeling, have not used it in conjunction withthe existing pore pressure estimation model. Because failure to properlycalculate pore pressure can threaten the health and safety of workersand the environment, a method to properly mitigate these concerns andaid in the economic recovery of natural resources is desirable.

SUMMARY OF THE INVENTION

The disclosed invention describes a method for determining the pressureat various depth points in a proposed oil or gas well location thatconsiders certain thermodynamic properties. These properties nowconsidered include thermal conductivity at different points within theproposed well and the heat flux at those points. These different datasets provide more information that can lead to a more effective,efficient and safe drill of the well.

In this method, the user creates several plots of data that is relatedto the depth of the proposed well. Included charts include the depth ofthe well against temperature, resistivity, and pressure. The pressure ofthe various points is analyzed using both the Eaton method and the DWCmethod. Using the pressure and resistivity, the thermal conductivity andheat flux can be determined for different depths. Based upon thegenerated graphs, the user can more accurately estimate the location ofthe Top of Geopressure (TOG), changes in pressure mechanism dominancebelow the TOG, as well as the possible location of hydrocarbons withinthe proposed well location.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pressure versus temperature plot of three wells that werepreviously drilled. Said wells are used as examples throughout thisdisclosure.

FIG. 2 is a consolidated pressure versus temperature plot for all threewells that were previously drilled. There is also an enlargement of the“Transition Zone”, demonstrating the change from normal to abnormalpressure.

FIG. 3 is resistance versus depth plot for one of the three wells.

FIG. 4 is an exemplary Drilling Well Control (DWC) resistivity overlayplot.

FIG. 5 is an exemplary geothermal gradient chart.

FIG. 6 is a composite plot of formation thermal conductivity, heat fluxthrough formation, and the normalized plot of dP/dT using Eaton's andDWC methods, side by side for well #1 in the described field example.

FIG. 7 is a structural map of the field for the three wells, showing thethree wells and the fault.

FIG. 8 is a basin simulator generated chart that compares pore pressure,excess pressure, heat flow, and geological age in millions of years forwell #1 in the field.

DETAILED DESCRIPTION OF THE INVENTION

The method described herein is a new method for analyzing pore pressureduring pre-drilling planning for crude oil and natural gas wells inorder to perform higher accuracy basin modeling. This novel method firstdevelops and applies the concept of thermal equilibrium in thepressure-temperature space. Basin modeling is then used to analyze porepressures along the depth of the interest and evaluate the effectivenessof seals as a barrier to heat flux. Data has suggested that an effectiveseal ideally prevents the leakage of pressure and temperaturesimultaneously from the system.

Eaton's work is used as the foundation for correlating the ResistivityLog (ohm-meter) values in normal and abnormal pressures across the SP9-mv) values of shale through the following, known equation (hereinafter“Eaton's Correlation”):P/D=S/D−0.535(observed shale resistivity/normal resistivity)^(1.2)In Eaton's Correlation, P/D, S/D, and 0.535 represent pressure gradient,overburden gradient, and normal effective stress value, respectively.Eaton's work developed a simple relationship that predicts the formationpore pressure by knowing the normally pressured compaction treadline,the observed resistivity/conductivity data and a relationship forformation overburden stress. Eaton's Correlation is also another form ofTerzaghi's effective stress theory, which is correlated to Normal andAbnormal resistivity values. Because those having skill in the art arefamiliar with Eaton's Correlation and its simplicity, and resistivityvalues give better estimates of normal/abnormal pressures (as comparedto other log data), this equation was selected to represent the GulfCoast compaction process.

The temperature-depth relationship suggests that temperature gradientincreases with depth in a linear fashion. Pressure is a function ofdepth and increases at deeper levels, thus this method considers that anover-pressured region in a field could exhibit high temperatures. Thislinear relationship between pressure and temperature defines theequilibrium of the system and is used to draft a pressure-temperatureplot.

The earth, containing various materials (e.g., shale, sandstone, salt,clays, minerals, limestone, dolomite, and chert), is subject to avariety of temperatures and pressures to such a degree that the earthacts like a reactor. A number of different reactions may occur,including processes that lead to abnormal Formation Pore Pressure todevelop. In these processes, the reactions obey the followingfundamental law:ΔG=ΔH−TΔS=ΔVP−TΔS  (“Equation 1”)In this equation, ΔG (Gibbs free energy) is the energy available toperform work. If ΔG is negative, the reaction will be instantaneous. IfΔG is positive, the reaction will not be instant, but will require asupply of additional energy in order to create a reaction. If ΔG equalszero, the reaction is considered to be at its “equilibrium state.” ΔHrepresents the change in enthalpy, or total heat content, of a system,wherein ΔH is equal to the sum of the internal energy and the product ofpressure multiplied by the volume. T represents the temperature at anyformation depth, and ΔS represents the change in entropy of the system.Entropy is the thermodynamic quality that represents the unavailabilityof a system's thermal energy for conversion into mechanical work, whichis often interpreted as the degree of disorder or randomness in thesystem. As those having skill in the art will recognize, Δ representsthe difference between two conditions. In order to determine the changesin the differences, those skilled in the art would perform thederivative of the above Equation 1, while keeping ΔV and ΔS constant,producing:dΔG=dPΔV−dTΔS  (“Equation 2”)

At Equilibrium Conditions, where there is no change in the ΔG, dΔGequals zero. Thus at Equilibrium Conditions, dPΔV−dTΔS=0. Expanding thisequation results in: dPΔV=dTΔS. Dividing both sides of this equation bydT results in: (dP/dT) ΔV=ΔS. Then, when dividing both sides of theequation by ΔV, those skilled in the art will recognize that the resultis Clapeyron's Equation:(dP/dT)=ΔS/ΔV

A careful examination of Clapeyron's Equation indicates that a plot ofpore pressure versus temperature generates a curve whose slope is equalto dP/dT, and that slope is also equal to ΔS/ΔV, indicating that theslope is a measure of energy per unit volume—or, pressure. This pressureis the additional pore pressure that is induced by temperature. Thisdisclosed invention tracks the deviations from equilibrium conditions asthe user drills from the surface to any desired depth. As ademonstrative of this method, understood to be an example alone, thethermal equilibrium of three wells were studied in the field. FIG. 1shows an example of a P-T plot for the field wells.

Next, this method consults the resistivity log for the site where thewell is being planned. For oil and gas well drilling, resistivitylogging is often used to assist in determining how porous the rockmaterials are. Resistivity logging is a known method of well loggingthat characterizes the rock or sediment by measuring its electricalresistivity. Most rock materials, especially those where oil and gaswells are drilled, are natural insulators, while their enclosed fluidsare conductors (with the exception of hydrocarbon fluids). When aformation is porous and contains salty water, the overall resistivitywill be low. However, if the formation contains hydrocarbon, or containsvery low porosity, the resistivity will be high. This logging alerts theuser as to whether the formation is permeable or not, as well asadditional data that can be used to calculate the temperature at a givendepth. In an additional embodiment, the relativity log and entire welllog is already available from outside sources.

After the resistivity data is collected, a plot must be made of theresistivity versus the depth, an example of which is seen in FIG. 3.Using the resistivity logs, at the bottom of the tangent (slope line),the user will establish shale baseline for the depth interval ofinterest on the spontaneous (“SP”) track. For the normal compactionregion, the user selects any shale resistivity point on the shalebaseline where the slope of the SP increased downward to its lowestpoint and the corresponding slope on the resistivity track reducestowards the bottom of the shale resistivity, as shown in FIG. 3. Thisprocess is repeated for the rest of the points selected by the user fromthe resistivity log. Using these data points, a plot of resistivity v.depth graph similar to that seen in FIG. 3 is produced. On that samegraph, the user plots the normal compaction trend line (“NCTL”) toindicate deviation from the normal compaction at sections below thenormal trend. The NTCL represents the sonic and resistivity values ifthe pore pressure was normal (hydrostatic), and methods for calculatingthe NCTL are known in the art. The resistivity value (R(sh normal)),represent the normal shale resistivity values. The plotted resistivityvalues that deviate from the normal values represent the observed shaleresistivity values.

Using the information obtained through available well logs or byperforming well logging, the user will then identify the Top ofGeopressure by locating and estimating the magnitude of pressure atdepth in the normal and transition to abnormally pressured zones. UsingEquation 1, the resistivity points from the previous chart can be usedto determine the pressure measured in psi. The user then applies thepressure calculations and the ratio of observed shale resistivity inabnormally compacted zones and the shale resistivity in the normallycompacted zones to Eaton's Correlation. For the field example, the“normally” compacted zone was defined as shale resistivity where the mudweight is 9.0 ppg, and the pressure versus depth plot for the fieldwells can be seen at FIG. 2. In FIG. 2, the Transition Zone is shown asresiding between the two horizontal lines indicating the Top ofGeopressure and Base of Geopressure. In that Transition Zone, there ispresent a double slope, indicating the existence of at least twodifferent pressure regimes within the same Transition Zone. Discoveringthe actual pore pressure content and the corrected fracture pressure ofthe Transition Zone is an important step, as the accurate prediction ofthe pore pressures and fracture gradients is necessary for properdrilling of wells.

Next, it must be understood that resistivity or conductivity is relatedto thermal energy (i.e., Gibbs free energy), through the followingrelationship, known to those skilled in the art as the “Nerst Equation”:

$E = {E_{s} - {\left( \frac{RT}{nF} \right){{Ln}\left( \frac{R_{1}}{R_{2}} \right)}}}$In the above equation, E is the cell potential energy (voltage energy,measured in Joules/Coulomb) at any given state in the earth, E_(s) isthe standard state potential energy (voltage energy) at standardpressure and temperature, R=8.314 is the universal gas constant inJules/mol-degree Kelvin, n is moles of flowing electrons, F or Faraday'sconstant equals 96,485 Coulombs per moles of electricity, and Qrepresents the reaction quotient in the earth reactor. The NearstEquation can be rewritten in terms of its thermodynamic energyequivalent:

$E = {E_{s} - {\left( \frac{RT}{nF} \right){LnQ}}}$${\Delta\; G} = {{\Delta\; G_{s}} - {\left( {- \frac{RT}{nF}} \right){LnQ}}}$${\Delta\; G} = {{\Delta\; G_{s}} + {\left( \frac{RT}{nF} \right){LnQ}}}$By multiplying both sides of the above equation by nF, the user obtains(hereinafter Equation $):nFΔG=nFΔG _(s)+(RT)LnQComparing the Nearst Equation to the above thermodynamics energy form ofthe equation, it is noted that ΔG=−nFE and ΔG_(s)=nFE_(s).

The user then takes the thermodynamic equilibrium condition as thenormally pressured zone and the conditions which deviate fromequilibrium as the abnormally pressured zone. This inventionincorporates the thermally induced abnormal pressure locations—the Topof Geopressure and Base of Geopressure positions along the depth—asaccurately as the data allows, and calculate, as accurately as the datawill permit, the magnitude of the pore pressure and the fracturepressure at each depth. In order to find the equilibrium, the aboveEquation $ to consider that at equilibrium, ΔG=0. Consequently, the termQ (reaction quotient) becomes K, the equilibrium constant, indicatingthat the system is in equilibrium or a normally pressured zone.

${\Delta\; G} = {{{\Delta\; G_{s}} + {\left( \frac{RT}{nF} \right){LnQ}}} = {0\mspace{14mu}{at}\mspace{14mu}{equilibrium}}}$Then Q=K, or the standard normal condition of the thermal energy:ΔG _(s) =−RTLnK

To then augment the P-T plot process, the known DWC method ofcalculating formation pore pressure is used. Using a DWC compositeresistivity trend line overlay, an example of which can be seen at FIG.4, the user plots the resistivity points on three cycle semi-log graphpaper. In the preferred embodiment, the resistivity points are plottedusing the middle cycle on the semi-log paper. Construction of the DWCoverlay, shown in FIG. 4, is based on assumed Gradients of G=0.465Psi/ft salt water at depth and temperature, 1.0 psi/ft overburden, and adata base that includes temperature effect provided by the followingequation (hereinafter “Equation 2”):

$\frac{R_{a}}{R_{n}} = {1.87\left( {1.0 - G} \right)}$

Next, the user draws the mud weight lines on the same semi-log paper,and then determines the associated mud weight of each resistivity pointusing the following equation. The mud weight is the density of thedrilling fluid and is normally measured in pounds per gallon (“ppg”).The mud weight is then converted from ppg to equivalent pressures inpsi. This pressure will be referred to as the Drilling Well Control(“DWC”) Pressure. The conversion is performed using the followingequation:DWC Pressure=0.052(Mud Weight)(Depth)

To construct the P-T equilibrium diagram, the user must estimate thetemperature gradient. This estimate can be done using thermal logs,logging while drilling, by using standard charts available in theindustry, such as that seen in FIG. 5, or by using the followingequation and the information recorded on the resistivity log heading:

$\frac{\frac{dT}{dZ}}{100\mspace{14mu}{ft}} = \frac{T_{2} - T_{1}}{X_{2} - X_{1}}$In this equation, dT/dZ is the temperature gradient (° F./100 ft), X₂ isthe depth (in feet) of the interest whose temperature is beingcalculated, X₁ is the depth whose temperature is already known, T₁ isthe temperature at X₁ depth, and T₂ is the temperature at X₂ depth.

To generate the P-T plot, it is necessary next to establish the thermalequilibrium of the particular interest location. The user plots the DWCpressure versus temperature three times, one each for the normal,transition zone, and abnormal pressure regions. An equation is then fitto each region by fitting a trend line to the individual curves on thegraph. Then the user chooses an equation with the highest R²(Coefficient of Determination or R squared) value as the “best-fit”equation.

Then the Eaton's and DWC results are both plotted, along with thethermodynamic properties of the formation (e.g., thermal conductivityand heat flux (flow) at each depth point, in one diagram, as shown inFIG. 6. To make the data from the Eaton's correlation and the DWC methodcompatible, the data must be normalized before generating the P-T plots,specifically the slopes of each segment in the normal (equilibrium),transition (deviation from equilibrium), and abnormal (deviation fromequilibrium) zones. In the preferred embodiment, the Z-scorenormalization method is used; however, those having skill in the artwill recognize that other normalization methods can be applied. Tonormalize the data using the Z-score method, the mean (M) of the dP/dTvalues is calculated. Then the standard deviation for all of the dP/dTvalues is determined using the following equation:Standard deviation={Σ(Y _(n) −M)²/(N−1)}^(1/2)In the above equation, N is equal to the number of data sets and Y_(n),represents the particular dP/dT value. To calculate the Z-score, thefollowing equation is used:

$\lbrack Z\rbrack_{n} = \frac{{Y(n)} - M}{SD}$The Z-score values represent the normalized dP/dT values. The user thenplots the normalized Eaton's gradient and the DWC Pressure gradient onthe same plot in order to identify the depth that compaction inducedpressure is significant and how much thermally induced pressure ispresent. This change in induced pressure dominance, occurs after thesystem achieves “Thermal Equilibrium” i.e. where the Eaton's gradientand the DWC Pressure gradient plot cross each other (Crossover Point orEquilibrium Point) as seen in FIG. 6. Each segment of the normalizedslope (dP/dT) is fit using a best fit equation. By plotting both thenormalized Eaton's dP/dT and DWC dP/dT side by side, the user pinpointswhere at depth and by how much the thermally induced pressure dominatesand determines where and by how much the compaction induced pressuredominates.

With the data normalized, the user determines the lithology compositionof the location of interest. Lithology composition is determinedvisually by estimating how much sand and shale the rock is made from atany depth of interest, and can be determined using a spontaneous (SP)log using the following steps. First, the user establishes a baselinefor clean sand and shale. Next, using the SP track on the resistivitylog, the user visually estimates how much reduction in shale content ispresent. The user then plots the shale resistivity values on a sheet ofsemi-log paper against the dept. Mud weight lines, in pounds per gallon,are then drawn on the semi-log paper using the DWC resistivity overlay.These mud weight values are then converted into the equivalent pressurein PSI. In an alternative embodiment, lithology compositions are insteadgathered from cores or cuttings data.

To calculate the thermal conductivity, known vertical thermalconductivity values for standard shale and sand values are reviewedalongside the lithology compositions. For ease of calculation,temperatures are converted from degrees Fahrenheit to Kelvin with theexception of the dP/dT plot, which will remain in degrees Fahrenheit.Feet are also converted to meters, with the exception for P-T and thenormalized dP/dT plots. Then, using the percentages of the rockcomposition, the thermal conductivity can be determined. For example,the thermal conductivity for typical shale is 1.64 Watts/meter-Kelvinand sandstone is 3.95 Watts/meter-Kelvin. For a 60 percent shale and 40percent sand composition, the following thermal composition is found:(1.64×0.6)+(3.95×0.4)=2.564 Watts/meter-KelvinTo calculate heat flow, the following equation can be used:

$q = {- {\lambda\left( \frac{dT}{dZ} \right)}}$In the above equation, q represents heat flow (flux), λ is the thermalconductivity, and dT/dZ represents the Geothermal gradient. The negativesign indicates heat flow is from the hotter to the colder region.

The user then places the graphs for thermal conductivity, heat flow, andthe combined normalized equilibrium dP/dT next to each other as seen inFIG. 6. Reviewing the normalized equilibrium dP/dT plot, the normallypressured zone (at equilibrium), show the DWC dP/dT is significantlyvoid of noise; however, the Eaton's dP/dT shows some noise in thenormally compacted zone. Consequently, the DWC signal can be used tofilter noise from Eaton's dP/dT through convolution. In the normalcompaction section of the formation, the dP/dT trend indicates that theeffect of temperature is weak and the effect of compaction in generatingpore pressure is dominant and strong.

The first crossover of the DWC dP/dT and Eaton's dP/dT lines(hereinafter “First Crossover”) provide the exact location of the Top ofGeopressure, which is 10,137 ft in the present field example. Below thisdepth of crossover point, the user discovers that in the upper part ofthe Transition Zone, the effect of temperature becomes stronger anddominant in generating abnormal pore pressure as the DWC plot deviatesto the right.

In the Transition Zone, at least three slopes are present, indicating tothe user that each one requires a specific mud weight to balance theformation pore pressure, and correctly estimate the fracture pressurewithout exceeding the Formation Fracture Pressure. In the TransitionZone, the majority of the upper part of the zone is dominated bythermally induced pore pressure. After the second crossover of the DWCdP/dT and Eaton's dP/dT lines (hereinafter “Second Crossover”), the usercan see that the compaction trend becomes the dominant force indeveloping the formation of pore pressure and formation fracturepressure.

The thermal conductivity and the heat flux plots demonstrate non-eventsin the normally compacted segment of the formation, which is atequilibrium. This behavior confirms the behavior of the dP/dT plot inthe “normally compacted zone.” In contrast to the neutral behavior inthis segment, significant changes can be seen in the Transition Zone,where the user can observe a number of incidents. First, the heat fluxshows a significant change in amplitude at the Top of Geopressure, whichis located exactly at the point of First Crossover. Second, at the pointof First Crossover, the thermal conductivity of the formation,especially within the upper part of the Transition Zone exhibits asignificant change in amplitude. Thus, the invention permits the user tosee that both observations of the dP/dT confirm the effect of thermalproperties in generating the thermally induced pore pressure andconsequently formation fracture pressure in the upper part of theTransition Zone. The user can now take thermal conditions into accountwhen planning the well drilling.

An additional incident evident on the heat flux and thermal conductivityplot is that the amplitude gradually diminishes after the SecondCrossover. This observation demonstrates that in the lower part of thetransition zone, the compaction induced pore pressure becomes dominantand the thermally induced pore pressure becomes weaker.

Further, in FIG. 6, the plot of thermal conductivity at point “a” andthe heat flux at point “b” indicate another useful feature of thisinventive method—the formation at these points is a “gas producing”formation. When the amplitude of these two plots increases together onthe right, in the same direction, it is an indication of the existenceof a hydrocarbon reservoir, since gases cool sand much differently thanliquids. In short, the cooling effect of the reservoir fluids, the typeof reservoir fluids, and the maturity of the hydrocarbons within thespecific thermal windows control the amplitude of the two thermalproperty plots in FIG. 6.

Now that the above properties of the well have been determined, the userinputs these features into a geological basin simulator. In oneembodiment, a one dimensional simulator, such as BasinMod (a commercialsimulator developed and marketed by Platt River Associates (PRA)) isused. However, as heat flow can be in both vertical and horizontaldirections in the earth's subsurface, a three dimensional simulatorcould also be used. Those having skill in the art will recognize that abasin could be simulated without the use of software, or through othersoftware available in the art currently or in the future. Continuingwith the field example, the structural map of the field is shown in FIG.7, including a ground fault present in the land, and the outcome of thesimulation is shown in FIG. 8.

The simulation results seen in FIG. 8 for well #1, which was drillednear the fault depicted in FIG. 7 reveals several key pieces ofinformation that would have been unavailable without the methoddisclosed herein. First, the start of the increase in pore pressure issynonymous with heat flow out of the system, as seen between 40-25 MY(Point A). This indicates the storing of more heat in the formation atPoint A. The rise in excess pressure plot is synonymous with thedecreasing heat flow out of the system (Point B). This is additionalevidence of storing heat and buildup of thermally induced pore pressureat Point B.

40 MY is the age when Jackson formation formed (Point C). The Jacksonformation is a “geological seal” in the example field. The formation ofthe seal happens at approximately 170° F., indicating that anappropriate temperature window for the continued precipitation oflimestone (referred to as “het limestone”). In addition to the shaleformation, the limestone seal location is very close in depth to the Topof Geopressure seen in FIG. 2.

Heat energy builds up until 24 MY and a temperature of approximately190° F. At this point, heat flow out of the system rises. This indicatesthat the seal leaked at that temperature and time due to excess porepressure build up. This is analogous to a relief valve openingautomatically to relieve a thermally induced pressure.

The relief valve seen in FIG. 7 is a fault. The fault and broken sealopen the pathway to migration of fluids to the other parts of thestructure.

As demonstrated in this disclosure, by mapping the temperature increaseat deeper depths within the subsurface along with considerations for theenabling conditions of the environment present, excess pressure isinduced and can now be accounted for in planning well drilling.Hydrocarbon bearing formations analyzed in wells in the field exampleindicate a potential economic benefit by using this method to identifyhydrocarbon flow to the surface. Considering this, it is understood thatthis approach can be used to locate hydrocarbon reservoirs, similar tohow the formation petrophysical properties such as resistivity andporosity, combined with biomarkers, are used today in formationevaluation.

The described features, advantages, and characteristics may be combinedin any suitable manner in one or more embodiments. One skilled in therelevant art will recognize that the varying components of this designmay be practiced without one or more of the specific features oradvantages of the particular embodiment. In other instances, additionalfeatures and advantages may be recognized in certain embodiments thatmay not be present in all embodiments.

The invention claimed is:
 1. A method for improved safe drilling of awell, wherein when an energy available to perform work equals zero, awell depth point is measured at equilibrium; wherein at equilibrium, aplot of pore pressure of the well at a particular depth point willgenerate a curve with a slope equal to a measure of energy per unitvolume, which will be defined as the additional pore pressure that isinduced by temperature at said depth point; said method comprising: (a)determining a resistivity of one or more depth points recorded for alocation of a potential well basin; (b) creating a graph that plots theresistivity of the potential well basin against the depth of thepotential well basin, wherein a normal compaction trend line is alsoplotted on the same graph; (c) creating a pressure versus temperatureplot that plots the potential well basin's pressure against the depth ofthe basin by calculating the pressure at the various depth pointsplotted on the said resistivity against depth plot; (d) defining atransition zone as a point between a top of the geopressure and a-bottomof the geopressure; (e) determining one or more slopes of energygradient within said transition zone to determine one or more pressureregimes within the transition zone; (f) relating the resistivity of theparticular depth point to thermal energy, wherein that relation is thenrewritten in the terms of its thermal equivalent; (g) calculatingformation pore pressure at the various depth points previouslyconsidered and evaluated using a DWC method; (h) normalizing datagenerated from the DWC method and the previously generated pressuredata; (i) plotting the normalized DWC method-generated data on the sameplot as the previously generated pressure versus temperature plot; (j)determining the lithology composition of the location of interest from anormalized data generated from the DWC method and the pressure data; (k)calculating a heat flux and a thermal conductivity of the proposed wellbased upon the lithology composition; (l) determining the top ofgeopressure to be the point at which a plot of the DWC method-generateddata intersects the pressure versus temperature plot for the first time;(m) entering the top of geopressure, pressure, and other thermalconditions into a basin simulator to generate a simulated basin forplanning; (n) drilling a well basin, wherein during said drilling, anydeviations from equilibrium are tracked to reduce drilling costs andincrease safety.
 2. The method of claim 1, wherein the resistivity ofthe various depth points it determined through resistivity logging. 3.The method of claim 1, wherein the basin is manually simulated.
 4. Themethod of claim 2, wherein the resistivity logging is performed usingwire-line or logging while drilling systems.
 5. A method for improvedsafety for drilling of a well, wherein when an energy available toperform work equals zero, a well depth point is measured at equilibrium;wherein at equilibrium, a plot of pore pressure of the well at aparticular depth point will generate a curve with a slope equal to ameasure of energy per unit volume, which will be defined as theadditional pore pressure that is induced by temperature at said depthpoint; said method comprising: (a) determining a resistivity of one ormore depth points recorded for a location of a potential well basin; (b)creating a graph that plots the resistivity of the potential well basinagainst the depth of the potential well basin, wherein a normalcompaction trend line is also plotted on the same graph; (c) creating apressure versus temperature plot that plots potential well basin'spressure against the depth of the basin by calculating the pressure atthe various depth points plotted on the said resistivity against depthplot; (d) defining a transition zone as a point between a top of thegeopressure and a bottom of the geopressure; (e) determining one or moreslopes of energy gradient within said transition zone to determine oneor more pressure regimes within the transition zone; (f) relating theresistivity of the particular depth point to thermal energy, whereinthat relation is then rewritten in the terms of its thermal equivalent;(g) calculating formation pore pressure at the various depth pointspreviously considered and evaluated using a DWC method; (h) normalizingdata generated from the DWC method and the previously generated pressuredata; (i) plotting the normalized DWC method-generated data on the sameplot as the previously generated pressure versus temperature plot; (j)determining the lithology composition of the location of interest from anormalized data generated from the DWC method and the pressure data; (k)calculating a heat flux and a thermal conductivity of the proposed wellbased upon the lithology composition; (l) determining the top ofgeopressure to be the point at which a plot of the DWC method-generateddata intersects the pressure versus temperature plot for the first time;(m) identifying a point of peak amplitudes of the thermal conductivityand heat flux; (n) defining a depth point of the peak amplitudes ofthermal conductivity and heat flux to locate a hydrocarbon reservoir;(o) drilling a well basin, wherein during said drilling, any deviationsfrom equilibrium are tracked to reduce drilling costs and increasesafety.